Mercurials are potent neurotoxins, which localize to both neurons and glia within the central nervous system and elicit a range of deleterious actions. Sodium ethylmercurithiosalicylate (thimerosal) is a widely used ethyl mercury containing preservative used in over-the-counter medications, cleaners and cosmetics. Recent concern has been raised on the use of thimerosal in over 30 vaccines licensed in the United States. With the addition of several important vaccines over the last few years, exposure to mercury has increased among infants, leading some investigators to suggest an association between thimerosal exposure and autism. There is limited toxicological information regarding ethyl mercury; therefore, estimates of health risks from thimerosal exposure have been based on mechanistic studies of methyl mercury, a close chemical relative about which much is known. These estimates may actually underestimate the toxicity of ethyl mercury containing agents. The wide use of thimerosal makes understanding the mechanism(s) of its toxicity a significant human health issue. The overall goal of this project is to investigate the mechanism by which thimerosal causes neuronal cell death. The hypothesis to be tested is that thimerosal results in dose-dependent activation of specific signaling molecules and redox-sensitive transcription factors known to activate pro-death genes in neurons. If this hypothesis is correct then pharmacological intervention should attenuate toxicity as a result of thimerosal exposure. Using a human neuroblastoma cell line, SK-N-SH, this project will test the hypothesis in four specific aims. Aim 1 will identify in a dose-dependent manner the predominant cell death pathway (apoptotic versus necrotic) associated with thimerosal exposure and to determine if it is associated with an increase in reactive oxygen species and caspase-3 dependent. Aim 2 will determine if cell death is mediated through an AP-1-dependent pathway. In addition, this specific aim will establish the role of c-Jun-N-terminal kinase; an enzyme, which phosphorylates and activates AP-1, in thimerosal-mediated neuronal death. Aim 3 will determine if the cell death pathway is mediated through an NFkappaB-dependent mechanism. Aim 4 will determine if thimerosal toxicity can be attenuated by the administration of S-adenosylmethionine, an enzyme which increases endogenous levels of glutathione. This project will generate mechanistic data on thimerosal neurotoxicity and potentially identify specific targets for pharmacological intervention.